Superconductivity at the flip of a switch

Researchers report the development of a superconducting system that we can …

Superconductivity research has produced a recent flurry of newly observed phenomena, including a paper, covered last week by Nobel Intent, describing superconduction that occurs when two non-superconducting materials share an atomically perfect interface. Now we can add a new paper to the list of superconductivity breakthroughs, as researchers have now induced superconductivity in a material with no superconductive transition by using an electrical field in a unique transistor setup.

Superconductivity is dependent on the charge carrier density—there must be enough electrons there to get the job done, regardless of how perfect a material is or how cold it is. Manipulating charge carrier density is the basis of the semiconductor industry, where chemical dopants and electrical fields alter the conductivity of materials, enabling us to build transistors. The generation of sufficient voltage to get a superconductive transition out of an insulator is often accompanied by dielectric breakdown, where the electrons are ripped from the atoms they orbit, causing a brief spike of conductivity and, ultimately, the failure of the material. You can see this behavior when the air, which is generally insulating, is chemically rearranged in the dielectric breakdown caused by a lightning bolt.

To get the charge carriers needed for superconductivity in an insulator, researchers made a modified electrochemical cell—a battery—and replaced an electrode with a perfect crystal of SrTiO3. When they applied an electrical current to the cell, positive charges built up in the electrolyte near its interface with the SrTiO3. To balance the buildup of positive charges, negative charges in the SrTiO3 would migrate to the surface, creating a thin layer with a high density of charge carriers. By cooling the whole system down to a chilly 0.4K, they were able to observe a superconductive transition.

Similar systems have been developed previously, but always using a material that had inherent superconductivity. The electric field could then slightly modify the temperature of the superconductivity transition.

Although this new superconducting material isn’t as earth-shattering as the discovery of high-temperature superconducting oxides in the mid-80’s, it does point out our fundamental lack of understanding of the intricacies of superconductivity. Superconductivity has generally been an innate material property, but developments like this one, and the superconductivity observed at material interfaces, represent some of the first steps towards the engineering of superconductive systems that we can actually manipulate.